You must read American Lawbreaking at Slate.

This series explores the black spots in American law: areas in which our laws are routinely and regularly broken and where the law enforcement response is … nothing. These are the areas where, for one reason or another, we've decided to tolerate lawbreaking and let a law—duly enacted and still on the books—lay fallow or near dead....

The importance of understanding why and when we will tolerate lawbreaking cannot be overstated. Lawyers and journalists spend most of their time watching the president, Congress, and the courts as they make law. But tolerance of lawbreaking constitutes one of the nation's other major—yet most poorly understood—ways of creating social and legal policy. Almost as much as the laws that we enact, the lawbreaking to which we shut our eyes reflects how tolerant U.S. society really is to individual or group difference. It forms a major part of our understanding of how the nation deals with what was once called "vice." While messy, strange, hypocritical, and in a sense dishonest, widespread tolerance of lawbreaking forms a critical part of the U.S. legal system as it functions.

It has particularly interesting secions on the drug war and illegal immigration. If you're impatient, the key take away is in the introduction.

Why are there dead zones in U.S. law? The answer goes beyond the simple expense of enforcement but betrays a deeper, underlying logic. Tolerated lawbreaking is almost always a response to a political failure—the inability of our political institutions to adapt to social change or reach a rational compromise that reflects the interests of the nation and all concerned parties. That's why the American statutes are full of laws that no one wants to see fully enforced—or even enforced at all.

This is the sort of compromise that allows people in places like Jena, LA and Paris TX to honestly feel they have no race problem.

This political failure can happen for many reasons. Sometimes a law was passed by another generation with different ideas of right and wrong, but the political will necessary to repeal the law does not exist. Sometimes, as we'll see with polygamy or obscenity, the issue is too sensitive to discuss in rational terms. And sometimes the law as written is a symbol of some behavior to which we may aspire, which nevertheless remains wholly out of touch with reality. Whatever the reason, when politics fails, institutional tolerance of lawbreaking takes over.

This is the purest description of the politics around racism, desegregation, integration, diversity or whatever term 'diversity' is scheduled to be superceded by, that I have ever seen. Anywhere.  The main addition I would make is to note that the political will to undo 1964 civil rights legislation did and does exist.